To study ‘atmospheric rivers,’ scientists take lab into skies off Washington coast

Originally published February 4, 2018 at 11:00 am
Updated February 4, 2018 at 8:37 pm

Researchers dropped parachute-equipped instruments from a jet on Friday, hoping the data one day will help improve how meteorologists predict bands of water vapor over the Pacific Ocean that are crucial to the West Coast’s water supply.

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Taking off from Everett’s Paine Field, a recent plane ride in the name of science could one day lead to improved methods for managing catastrophic flooding and droughts across the West Coast.

While the Pacific Northwest faced a heavy soaking of rain and snow Friday, a team of scientists was chasing the winter weather over the Pacific Ocean by jet, taking cutting-edge measurements in a mobile laboratory they say could someday improve weather modeling and forecasts.

In the high-tech, G-IV aircraft, used by meteorologists for hurricane tracking, the group had one high-altitude target: a long, narrow band of water vapor, called an “atmospheric river,” that dumps massive amounts of moisture. It was the last of three similar missions since Jan. 25.

“Exactly where they (atmospheric rivers) hit and when, and how strong they are, determines a lot about the precipitation — where the heaviest rains are in the region,” said mission director Marty Ralph, shortly before boarding the hourslong flight that took off about 25 miles north of Seattle.

“Going offshore to measure atmospheric rivers before they hit shore, we’ll have a better chance to improve the forecast.”

Winds associated with cyclones form the weather streams over oceans. When their moisture-laden air moves over mountain ranges, the water vapor rises and cools — resulting in heavy rain or snow.

Atmospheric rivers occur worldwide, but are especially significant on the U.S. West Coast, where they create 30 to 50 percent of annual precipitation, according to the National Oceanic and Atmospheric Administration (NOAA). They play a crucial role in the region’s water supply.

In the eye of Friday’s storm, the researchers dropped small, parachute-equipped instrument packages, called “dropsondes,” which mimic the tools meteorologists use to make weather forecasts from the ground.

Out of the jet, the dropsondes fell for about 15 to 20 minutes before reaching the ocean, along the way recording conditions ranging from temperatures to wind speeds to moisture levels.

The devices sent that information via satellite to the aircraft, where the scientists funneled it to a global storehouse of weather data.

Yearslong project

The flying missions are one of many steps in a massive, long-ranging research effort that will span years.

A multitude of factors can make models inaccurate in terms of real space and time.

“It’s quite a complex and sophisticated challenge to pull that off appropriately,” Ralph said. “There are just all sorts of ways for this to go wrong, and we need a lot of effort to work through how to make it right.”

After that, the team hopes the improved forecast modeling can help officials lower or mitigate threats of flooding and droughts.

Operators of dams could make better decisions for how much water to keep stored or to release downstream, Ralph said. Practices for managing reservoirs are many years old and generally do not rely on weather forecasts.

“These big storms is where the action is,” Ralph said. If they can be predicted more accurately, he said, maybe a reservoir operator could know when to keep more of that water collected behind the dam in case of a dry spell.

The Seattle-area aircraft is one of three in the data-collection project, which includes a variety of government and weather agencies, including the National Weather Service, the Air Force and NOAA.

Scientists chose the local spot for takeoff and landing because of the Seattle area’s proximity to portions of the air streams, which extend from Hawaii to California; Vancouver, B.C.; and Alaska.

Cold air from Alaska sometimes pushes south and interacts with the atmospheric rivers, and the G-IV aircraft out of Everett could measure that phenomenon, Ralph said.

Researchers in Hawaii and Northern California have been simultaneously using military jets with the same goal.

The effort to improve weather modeling is especially vital to drought-prone California, with its agriculture-dependent economy.

While briefing reporters on this winter’s unusually dry start last month, Grant Davis, director of California’s Department of Water Resources at the time, called for more improvements in long-range forecasting to help the state’s reservoir managers better operate dams for water supply and flood control.

Friday’s atmospheric river followed a series of wet-weather systems drenching Western Washington over the past couple of weeks, dumping up to 5 inches of rain in parts of the Seattle area, according to the weather service in Seattle. The moisture has increased the risk of landslides and flooding.

As of Friday evening, the service’s forecast determined rain, at least in the form of showers, would be likely throughout the weekend and Monday, with a flood watch in effect through late Monday night.

Material from The Seattle Times archives and The Associated Press is included in this report. Jessica Lee: 206-464-2532 or jlee@seattletimes.com